Perhaps the most challenging aspect of the Miller case was how to navigate the judicial role in a complex constitutional environment which is only partially regulated by law. While the dissenting judges were largely content to leave it to the political sphere to constrain executive power, and negotiate the respective authority claims of the UK Parliament, the devolved legislatures and the people via the referendum, the majority attempted to draw a sharp distinction between the legal and political constitutions.

In refusing to rule on the applicability of the Sewel Convention, the majority (with whom the dissenting judges agreed on this point) acknowledged the fundamental role of conventions in the constitution, but insisted that courts have no role to play in policing them.  They may “recognise” the operation of conventions where relevant to the resolution of legal questions, but cannot rule on their meaning or scope.

This approach is problematic, not least because it is strongly arguable that Sewel was relevant to the resolution of a legal question – namely the meaning of ‘constitutional requirements’ in Article 50 TEU – and because there are precedents which have ruled on the operation of conventions (for instance, the Evans case). Sewel is also an unusual convention since it now has statutory recognition.  The Supreme Court considered that section 2 of the Scotland Act 2016 was not intended to convert Sewel into a justiciable legal rule, but rather to “entrench it as a convention” (para 149). But this is a perplexing notion in the absence of any method of enforcing compliance with it, and a controversial decision in the context of the delicate state of UK-Scottish constitutional politics.

The most problematic issue is what happens next? The court emphatically did not say that Legislative Consent Motions are not required, as some of the reporting has suggested. However, in refusing to give any definitive guidance on the devolution issues – for instance, hinting, but not clearly ruling that an Article 50 Bill would affect devolved matters (paras 129 – 132) – the decision has set the scene for a political conflict in which the UK institutions have a legal advantage. How this will end is anyone’s guess.

Aileen McHarg is Professor of Public Law at the University of Strathclyde.

Click here for further analysis of the Supreme Court’s Miller judgment.

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